Sugars and the Origin of Life

Like DNA, the single-helix structure of RNA resembles a spiral staircase. The backbone of RNA is composed of a sugar. Credit: Darryl Leja/Access Excellence

Sugars give rise to enormous biochemical interest given the importance and diversity of the functions they carry out: they act as an energy storage system and serve as fuel for a number of biological systems; they form part of DNA and of ribonucleic acid (RNA) and, moreover, play a key role in cell processes. Recently interest in sugars has also been increasingly attracting the attention of cosmochemistry, more concretely, in the search for the fundamental matter of the origin of life in interstellar space.

Finding this would also help in the understanding of what the mechanism of the origin of life on Earth was. The most elemental of sugars, made up of 2 and 3 units of carbon, have already been found in interstellar molecular clouds and meteorites.

The sugar phosphate backbone (the "railing" of the "spiral staircase") consists of a chain of repeating units. Shown above are the backbones of RNA and of TNA. Image credit: Schöning et. al., 2001

Nevertheless, it has not been possible to date to detect more complex sugars in space, given the absence of precise information about their structure. This information is what the research laboratories have to provide.

There are numerous research teams to be first in the race to detect this sugar in gas phase, using high-resolution techniques. Problems have arisen in trying to vaporise it due to the thermal instabilities caused by loss of water.

“Only if you avoid the processes of decomposition on dehydration and manage to isolate the sugar, thus obviating the changes produced by neighbouring molecules, will you be in a position to characterise its structure”, explained Emilio José Cocinero, researcher at the Department of Physical Chemistry of the University of the Basque Country (UPV-EHU).

His latest research has become amongst the first worldwide to have managed to observe a sugar – a ribose – in the gas phase and to characterise a number of its structures. His article, “Ribose Found in the Gas Phase”, published by the Angewandte Chemie International Edition, was on the front cover of the April issue of the scientific journal and also highlighted in the on-line version.

In order to observe the ribose in gas phase, microwave spectroscopy was used combined with ultra-rapid laser vaporisation with ultraviolet light. Not only was it isolated and observed, but six different structures of the ribose were detected.

“Sugars are super flexible molecules that can take on many different configurations. We have managed to detect the six most stable structures of the free ribose”, explained the lead researcher.

However, all the structures detected show rings of six members, i.e. the structures involved are very different from those shown in RNA or ADNA ribose or its derivatives, where the rings are five-membered.

“Given that the genetic material has a different configuration, it is unlikely that the first living beings had ribose. Thermal instability and the preference for 6-member rings would appear to exclude the possibility that the first genetic material was made up of this sugar”, concluded Mr Cocinero.

With this door opened to the study of sugars in gas phase, it will be “easier” to obtain information on the role of sugars in the origin of the first living beings.